Activated hGH isohormones D and E were isolated by a new method capable of producing homogeneous species in amounts sufficient for growth assay in man. Human prolactin was prepared from amniotic fluid in 60 percent overall yield. From 10 1 of the fluid, 3 mg of a mixture of hPRL isohormones A, B, C and D free from protein contaminants was isolated. Another 3 mg of hPRL was of lesser purity. The method, for the first time, provides milligram amounts of the hormone required for isohormone separation for biochemical and physical-chemical purposes.